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examples.js
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examples.js
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// Copyright (C) 2010 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Example using the traits.js library.
// This file defines three abstractions:
// - an 'enumerable' trait that captures the commonalities of enumerable data types
// - a 'comparable' trait that captures the commonalities of comparable data types
// - an 'interval' data type that makes use of these traits
load('traits.js'); // provides Trait
/**
* makeEnumerableTrait(makeSeq) -> <anEnumerableTrait>
*
* @param makeSeq a function() -> Sequence
* where Sequence is an object c that understands c.push(elem)
* in order to append an element to the sequence
* @return an enumerable trait that can be composed with other traits
*
* This trait is 'incomplete'. It requires the composer to provide
* methods named 'forEach' and 'reverseEach':
* - forEach: function(fun) -> apply fun to each element and index of an enumeration
* - reverseEach: function(fun) -> like forEach, but enumerate in reverse
*/
function makeEnumerableTrait(makeSeq) {
return Trait({
// state required properties (optional, but informative)
forEach: Trait.required,
reverseEach: Trait.required, // needed for reduceRight only
// the trait provides these properties:
map: function(fun) {
var seq = makeSeq();
this.forEach(function(e,i) {
seq.push(fun(e,i));
});
return seq;
},
every: function(pred) {
var escape = {};
try {
this.forEach(function(e,i) {
if (!pred(e,i)) {
throw escape; // force non-local exit
}
});
} catch(e) {
if (e !== escape) throw e;
return false;
}
return true;
},
some: function(pred) {
var escape = {};
try {
this.forEach(function(e,i) {
if (pred(e,i)) {
throw escape; // force non-local exit
}
});
} catch(e) {
if (e !== escape) throw e;
return true;
}
return false;
},
filter: function(pred) {
var seq = makeSeq();
this.forEach(function(e,i) {
if (pred(e,i)) {
seq.push(e);
}
});
return seq;
},
reduce: function(fun, optInit) {
var result = optInit;
this.forEach(function(e,i) {
result = fun(result, e, i);
});
return result;
},
reduceRight: function(fun, optInit) {
var result = optInit;
this.reverseEach(function(e,i) {
result = fun(result, e, i);
});
return result;
},
asSequence: function() {
return this.map(function (e) { return e; });
},
})
}
// TEnumerable is an enumerable trait that implements all sequences
// returned by the higher-order functions as arrays
var TEnumerable = makeEnumerableTrait(function() { return []; });
/**
* TComparable provides common relational operators associated with
* comparable data types, given a definition for '<' and '=='.
*
* TComparable can be used for partially ordered data types. In this case,
* two elements a and b are incomparable if !(a <= b) && !(b <= a). For
* incomparable elements, the relational operators return 'false' and the
* min and max operators return 'undefined'.
*/
var TComparable = Trait({
'<': Trait.required, // this['<'](other) -> boolean
'==': Trait.required, // this['=='](other) -> boolean
'<=': function(other) {
return this['<'](other) || this['=='](other);
},
'>': function(other) {
return other['<'](this);
},
'>=': function(other) {
return other['<'](this) || this['=='](other);
},
'!=': function(other) {
return !(this['=='](other));
},
between: function(min, max) { // inclusive between
return min['<='](this) && this['<='](max);
},
min: function(aMagnitude) {
if (this['<='](aMagnitude)) {
return this;
} else if (aMagnitude['<'](this)) {
return aMagnitude;
} else {
return undefined;
}
},
max: function(aMagnitude) {
if (this['<='](aMagnitude)) {
return aMagnitude;
} else if (aMagnitude['<'](this)) {
return this;
} else {
return undefined;
}
}
});
/**
* makeInterval(min, max) -> an interval min..!max
*
* A constructor for an open interval data type.
* Open intervals are enumerable as arrays [min,min+1,...,max-1].
* Open intervals are partially ordered. 'less than' is defined as follows:
* min1..!max1 < min2..!max2 <=> max1 <= min2
*
* Note: the interval trait defines the required 'forEach' and 'reverseEach'
* methods for TEnumerable and the required '<' and '==' methods for TComparable.
* In return, it "inherits" all the higher-order methods of TEnumerable and
* all the derived relational operators of TComparable.
*
* In this particular example, the composed traits don't define properties
* with a common name, so there is no need for conflict resolution.
*/
function makeInterval(min, max) {
return Trait.create(Object.prototype,
Trait.compose(
TEnumerable,
TComparable,
Trait({
start: min,
end: max,
size: max - min - 1,
toString: function() { return ''+min+'..!'+max; },
'<': function(ival) { return max <= ival.start; },
'==': function(ival) { return min === ival.start && max === ival.end; },
contains: function(e) { return (min <= e) && (e < max); },
forEach: function(consumer) {
for (var i = min; i < max; i++) {
consumer(i,i-min);
}
},
reverseEach: function(consumer) {
for (var i = max - 1; i >= min; i--) {
consumer(i,max-1-i);
}
}
})));
}
// === unit tests ===
function testTraits() {
load('../../tests/unit.js');
var unit = makeUnitTest("TraitExamples", false);
function testSameArray(arr1, arr2, id) {
if (unit.compare(arr1.length, arr2.length, id+"isSameArray length")) {
for (var i = 0; i < arr1.length; i++) {
unit.compare(arr1[i], arr2[i], id+"isSameArray i="+i);
}
}
}
var i1 = makeInterval(0,6);
var i2 = makeInterval(7,10);
unit.compare(0, i1.start, "start");
unit.compare(6, i1.end, "end");
unit.compare(true, i1['<'](i2), "<");
unit.compare(false, i1['=='](i2), "i1 == i2");
unit.compare(true, i1['=='](i1), "i1 == i1");
unit.compare(5, i1.size, "i1 size");
unit.compare(true, i1['<='](i2), "i1 <= i2");
unit.compare(false, i2['<='](i1), "i2 <= i1")
unit.compare(true, i1['<='](i1), "i1 <= i1");
unit.compare(false, i1['>='](i2), "i1 >= i2");
unit.compare(true, i2['>='](i1), "i2 >= i1")
unit.compare(true, i1['>='](i1), "i1 >= i1");
unit.compare(false, i1['!='](i1), "i1 != i1");
unit.compare(true, i1['!='](i2), "i1 != i2");
unit.compare(true, i1.contains(0));
unit.compare(true, i1.contains(1));
unit.compare(true, i1.contains(5));
unit.compare(false, i1.contains(-1));
unit.compare(false, i1.contains(7));
unit.compare(true, i1.between(i1,i1), 'i1 between i1 and i1');
unit.compare(true, i1.between(i1,i2), 'i1 between i1 and i2');
unit.compare(false, makeInterval(2,4).between(i1,i2), '2..!4 between i1 and i2');
unit.compare(true, makeInterval(6,7).between(i1,i2), '6..!7 between i1 and i2');
unit.compare(i1, i1.min(i2), "i1 min i2");
unit.compare(i1, i2.min(i1), "i2 min i1");
unit.compare(i2, i1.max(i2), "i1 max i2");
unit.compare(i2, i2.max(i1), "i2 max i1");
unit.compare(undefined, i1.min(makeInterval(3,7)), "i1 min 3..!7");
unit.compare('0..!6',''+i1, "i1 toString");
testSameArray([0,1,2,3,4,5], i1.asSequence(), 'i1.asSequence');
testSameArray([1,2,3,4,5,6], i1.map(function(e,i) { return e+1; }), 'map i1');
testSameArray([0,1,2], i2.map(function(e,i) {return i; }), 'map i2');
unit.compare(true, i1.every(function(e) { return e <= i1.end; }), 'i1.every <= end');
unit.compare(false, i1.every(function(e) { return e%2 === 0; }), 'i1.every even');
unit.compare(true, i1.some(function(e) { return e === 3; }), 'i1 some 3');
unit.compare(false, i1.some(function(e) { return e < i1.start; }), 'i1 some < start');
testSameArray([0,2,4], i1.filter(function(e) { return e%2 === 0; }), 'filter even');
testSameArray([], i1.filter(function(e) { return false; }));
testSameArray(i1.asSequence(), i1.filter(function(e) { return true; }));
unit.compare(15, i1.reduce(function(sum, e) { return sum+e; }, 0), 'i1.reduce sum');
unit.compare(3, i2.reduce(function(sum, e, i) { return sum+i; }, 0), 'i2.reduce sum idx');
unit.compare('foo',
makeInterval(0,0).reduce(function(tot,nxt) { return 'bar'; },'foo'),
'0..!0.reduce');
unit.compare(15,
i1.reduceRight(function(sum, e) { return sum+e; }, 0),
'i1.reduceRight sum');
unit.compare('543210',
i1.reduceRight(function(str,e) { return str+e; }, ''),
'i1.reduceRight append');
unit.compare(3, i2.reduceRight(function(sum, e, i) { return sum+i; }, 0), 'i2.reduceRight sum idx');
return unit.testDone();
}
testTraits();